Polycarboxylate-containing antifreeze/coolant additive for reducing corrosion in heat rejecting aluminum

ABSTRACT

The present invention provides an antifreeze/coolant additive comprising polymeric polycarboxylates which reduces the corrosion rate of heat rejecting aluminum, and is effective at relatively low concentrations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to antifreeze/coolant additives and morespecifically to antifreeze/coolant additives comprising polycarboxylateswhich reduce corrosion in heat rejecting aluminum.

2. Description of the Prior Art

Antifreeze/coolant technology in North America uses silicate as acorrosion inhibitor. Silicates are particularly useful in protectingaluminum automotive cooling system components. The silicate corrosioninhibitors generally also use a phosphate, usually in the form of analkali metal salt, to help protect metal cooling system parts and alsoas a buffer to control the pH of the coolant. Often phosphate salts areused to help maintain a stable alkaline environment from which multiplecorrosion inhibitors can most effectively function.

Traditionally antifreeze/coolant is sold at nearly one-hundred percentglycol content. This concentrated packaging allows for flexibility sothat the user can dilute the antifreeze/coolant, as needed, withavailable water to obtain the required freeze/boil protection. However,corrosion protection is needed over the entire dilution range.

Today, in modern automotive engineering, many engine components arefabricated from aluminum. Engine coolants, primarily ethylene glycolbased solutions, must transfer heat from operating aluminum engineswhile inhibiting corrosion. Older automotive engines did not havealuminum components and thus, the traditional antifreeze/coolantcompositions may produce corrosion in heat rejecting aluminum oraluminum alloy components.

Certain polycarboxylate type materials have been disclosed forprevention of precipitates in antifreeze/coolant compositions. Forexample, U.S. Pat. No. 3,663,448 discloses scale inhibition forindustrial cooling waters using amino phosphonate and polyacrylic acidcompounds. U.S. Pat. No. 3,948,792 discloses an aqueous additive mixtureto reduce and modify the amount of silicate scale formed in automotivecooling systems.

European patent 245557 discloses the use of a variety of compoundsincluding sodium polyacrylate to prevent alkaline earth metal silicateprecipitation. U.S. Pat. No. 4,487,712 discloses the use of polyacrylicacid as a silicate stabilizer to inhibit gelation. Gelation is asilicate depletion mechanism which can occur separately from hard waterprecipitates.

In spite of these disclosures, there remains a need for anantifreeze/coolant additive which reduces corrosion in heat rejectingaluminum and aluminum alloys.

SUMMARY OF THE INVENTION

The present invention has met the above-described need by providing anantifreeze/coolant additive comprising polymeric polycarboxylates whichreduces corrosion in heat rejecting aluminum and aluminum alloys. Thisadditive is soluble in alcohol and alcohol/water mixtures, is compatiblewith other commonly used antifreeze/coolant components, does not corrodeor damage automotive cooling systems and is effective at relatively lowconcentrations.

It is an object to provide antifreeze/coolant additives which areeffective at reducing the corrosion of heat rejecting aluminum andaluminum alloys.

It is another object of the present invention to use polymericpolycarboxylates in silicate-phosphate type antifreeze/coolantcompositions to reduce the corrosion in heat rejecting aluminum andaluminum alloys.

These and other objects of the present invention will be more fullyunderstood from the following description of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an antifreeze/coolant additive comprisingpolymeric polycarboxylates which reduce corrosion in heat rejectingaluminum or aluminum alloys. This additive is soluble in alcohol andalcohol/water mixtures, is compatible with other commonly usedantifreeze/coolant components, does not corrode or damage automotivecooling systems and is effective at relatively low concentrations.

The preferred class of polymeric polycarboxylates are based onpolyacrylic acid (PAA) and/or polymaleic acid (PMA). These polymericpolycarboxylates are compatible with other components in the typicalantifreeze/coolant composition, and present no additional toxicity ordisposal concerns.

Other materials which are useful in the present invention includeBelclene water treatment additives from Ciba-Geigy, Colloid additivesfrom Colloids, Inc., Good-rite polyacrylates and Carbopol resins from BFGoodrich and the like, as exemplified in Table 1A.

The molecular weight distribution of useful materials may average aboutone hundred grams/mole to about three million grams/mole. Chemically,the materials should be based on polymers and copolymers of acrylic acidand maleic acid, including many modifiers such as alcohols.

The polycarboxylates used in the present invention have a molecularweight range of from about 500 to about 250,000, with a preferred rangeof from 500 to 12,000. More specifically, the most preferred additiveshave average molecular weights in the range of about 500 to about 4,000,and more specifically about 1300 to about 1800 and about 300 to about4600.

When reference is made to polycarboxylates within the context of thepresent invention it is understood to encompass those water-solublehomo- and copolymers having at least one monomeric unit containing C₃₋₆monoethylenically unsaturated mono- or dicarboxylic acids or theirsalts. Suitable monocarboxylic acids of this type are for example,acrylic acid, methacrylic acid, ethacrylic acid, vinylacetic acid,allylacetic acid, and crotonic acid. The preferable monocarboxylic acidsfrom this group are acrylic acid and methacrylic acid. A furthercomponent of the polycarboxylate comprises monoethylenically unsaturatedC₄₋₆ dicarboxylic acids, for example, maleic acid, itaconic acid,citraconic acid, mesaconic acid, fumaric acid, or methylenemalonic acid.The preferred acid is maleic acid.

Other organic substituents may be used as comonomers or as modifiersadded along the polymer chain. Examples of such are shown as Formula I.##STR1## where R=H or a secondary alcohol such as isopropanol, X=COOH,COO⁻ Na+, methylvinylether, isobutylene, vinyl acetate, acrylamide, orstyrene, with the proviso that when R=a secondary alcohol, X=COOH orCOO⁻ Na+, and when X=any other above referenced group, R=H. Thepreferred polycarboxylates are a copolymer of acrylic acid and maleicacid, or their sodium salts, said copolymer having a molecular weight of3000, and a sodium salt of polyacrylic acid modified with a secondaryalcohol such as isopropanol, said polymer having a molecular weight of4000.

The polycarboxylates used in the present invention are obtained bymethods well known to those skilled in the art. The general method ofsynthesis is via free acid radical polymerization. The polymerizationmay be carried out in an aqueous medium, in the presence ofpolymerization initiators, with or without regulants. The polymerizationcan take various forms; for example, the monomer(s) can be polymerizedbatchwise in the form of aqueous solutions. It is also possible tointroduce into the polymerization reactor a portion of the monomer(s)and a portion of the initiator, to heat the mixture in an inertatmosphere to the polymerization temperature and then to add theremaining monomer(s) and initiator to the reactor at the rate ofpolymerization. Polymerization temperatures range from 20° C. to 200° C.At temperatures above 100° C., pressure vessels are employed.

The carboxyl containing monomers can be polymerized in the freecarboxylic acid form, in the partial neutralized form, or completelyneutralized. The neutralization is preferably effected with alkali metalor ammonium base.

The polymerization initiators used are preferably water soluble freeradical formers such as hydrogen peroxide, peroxodisulfates and mixturesof the two. The polymerization may also be started with water insolubleinitiators such as dibenzoyl peroxide, dilaurylperoxide, orazodiisobutyronitrile. The polymerization may be carried out in thepresence of regulants. Examples of such regulants include water solublemercaptans, ammonium formate, and hydroxylammonium sulfate.

Examples of the polycarboxylates which may be used in the presentinvention are those marketed by BASF under the trademark SOKALAN®polycarboxylates, which are available in aqueous polymer solutions.

The polymeric polycarboxylate is effective at relatively lowconcentrations, generally about 100 to about 1000 ppm per total volumeof antifreeze/coolant. While particularly preferred additive, Sokalan®CP 10 S, has been shown to be particularly effective at about 0.15weight percent in a silicate-phosphate type coolant in reducing hotsurface aluminum corrosion, other levels of additive and differentpolycarboxylates may also be useful.

In addition to silicate-phosphate type coolants, these additives areuseful in silicate-borax, amine-phosphate, amine-borax, organicacid-phosphate organic acid-borax type coolants, and the like.

The most preferred antifreeze/coolant composition is asilicate-phosphate type having about 94% antifreeze grade glycols andabout 3% corrosion inhibitors, with the balance being water. Whileethylene glycol is preferred in the present invention, propylene glycoland mixtures of ethylene glycol and propylene glycol may also be used.

The corrosion inhibitors generally are a mixture of azole compounds,nitrate salts, defoamers and other constituents in addition to thestabilized silicate and phosphate salts. The stabilized silicatetechnology is disclosed in U.S. Pat. Nos. 4,370,255; 4,362,644 and4,354,002, all hereby incorporated by reference. Antifreeze/coolantcompositions are well-known in the art and many variations of theabove-described composition will be useful in the invention.

The following examples serve to further illustrate the present inventionand should in no way be construed as limiting the scope thereof.

EXAMPLES

ASTM D4340-84 is the standard test method for Corrosion of Cast AluminumAlloys in Engine Coolants Under Heat Rejecting Conditions. This test wasselected as a method to investigate the utility of polycarboxylates asgeneral corrosion inhibitors for heat rejecting aluminum. ASTM D4340-84simulates the real world operating condition of heat rejecting aluminum.Thermally influenced effects such as changing thermal coefficient ofexpansion and rates of mass transport can be reflected in this test. Itis of interest to identify materials which can reduce corrosion rates bythis test.

A silicate-phosphate based on antifreeze/coolant of pH 10.5 was selectedfor testing. The coolant is 94% antifreeze grade glycols, 3% corrosioninhibitors and 3% water. The corrosion inhibitors included nitratesalts, azole compounds, defoamer, caustic soda and alkali metalphosphates. Also included were stabilized silicate copolymers of thetype discussed in U.S. Pat. Nos. 4,370,255, 4,362,644 and 4,354,002, allof which are hereby incorporated by reference.

The coolant was evaluated by ASTM D4340-84. To this base coolant amodified polyacrylic acid was added at 0.15 weight percent. This gave animproved coolant which was also evaluated by ASTM D4340-84. Duplicateresults for each experiment and ASTM specified maximum weight loss areshown in Table 1. All rates are in milligrams/cm-cm/week.

                  TABLE 1                                                         ______________________________________                                                              Coolant +  ASTM                                         Specimen Tested                                                                           Coolant   Additive   Spec. To Pass                                ______________________________________                                        319-100               0.217      1.0                                          319-101               0.168      1.0                                          MS370       0.7008               1.0                                          MS574       0.6268               1.0                                          AVERAGE     0.6638     0.1925                                                 RESULT      PASS      PASS                                                    ______________________________________                                    

From Table 1, it can be seen that the polyacrylate containing coolantexhibited an average corrosion rate of 0.1925 mg/cm-cm/week while thebase coolant gave 0.6638 mg/cm-cm/week. This represents a reduction inaluminum corrosion rate of over three times.

The coolant containing Sokalan® CP 10 S was evaluated by theASTMD1384-87 standard test method. This is a corrosion weight loss testmethod for engine coolants in glassware. Weight change results for acontrol, 0.15 wt. % Sokalan® CP 10 S containing coolant and the ASTMspecifications required to pass are given in Table 2. All weight changesare in milligrams per coupon (mg/coupon).

                  TABLE 2                                                         ______________________________________                                                                         Base Coolant +                               Metal Coupon                                                                             Spec. to Pass                                                                            Base Coolant                                                                             Additive                                     ______________________________________                                        Copper     -10        -0.6       -1.1                                         2006 Solder                                                                              -30        +0.3       -0.6                                         Brass      -10        -2.4       -9.0                                         Mild Steel -10        +0.6       -0.1                                         Cast Iron  -10        -0.8       +1.8                                         Aluminum   -30        +6.1       +2.6                                         TEST RESULT           PASS       PASS                                         ______________________________________                                    

The addition of 0.15 weight percent of Sokalan® CP 10 S caused nosignificant corrosion to cooling system metals based upon the results ofTable 2. Table 2 shows that the base coolant and the modified coolantboth passed.

Whereas particular embodiments of the invention have been describedabove for purposes of illustration, it will be appreciated by thoseskilled in the art that numerous variations of the details may be madewithout departing from the invention as described in the appendedclaims.

What is claimed is:
 1. A glycol-based automotive antifreeze/coolantsolution which reduces the corrosion rate of heat rejecting aluminum oraluminum alloy including a corrosion rate reducing effective amount of apolycarboxylate additive which is at least one of (i) a sodium salt of acopolymer of acrylic acid and maleic acid, and (ii) a secondary alcoholmodified polyacrylic acid.
 2. A glycol-based automotiveantifreeze/coolant solution as in claim 1, wherein said polycarboxylateis a sodium salt of a secondary alcohol modified polyacrylic acid.
 3. Aglycol-based automotive antifreeze/coolant solution as in claim 1 or 2,wherein said polycarboxylate additive is present in an amount of about100 to 1000 ppm per total volume of the antifreeze/coolant solution. 4.A glycol-based automotive antifreeze/coolant solution as in claim 3,wherein said polycarboxylate has a molecular weight range of from about500 to about 250,000.
 5. A glycol-based automotive antifreeze/coolantsolution as in claim 1, wherein said polycarboxylate is a sodium salt ofan acrylic acid/maleic acid copolymer having a molecular weight of 3000.6. A glycol-based automotive antifreeze/coolant solution as in claim 1,wherein said polycarboxylate is a polyacrylic acid modified with analiphatic secondary alcohol.
 7. A glycol-based automotiveantifreeze/coolant solution as in claim 6, wherein said polycarboxylateis a sodium salt of a polyacrylic acid modified with an aliphaticsecondary alcohol having a molecular weight of
 4000. 8. A glycol-basedautomotive antifreeze/coolant solution as in claim 6 or 7, wherein saidaliphatic secondary alcohol is isopropanol.